1. Field of the Invention
The present invention relates generally to single crystal diamond manufactured by chemical vapor deposition (CVD). More specifically, the invention is concerned with high quality, ultratough single crystal CVD diamond doped with boron. The invention also relates to methods of manufacturing the same.
2. Description of Related Art
The fabrication of high quality single-crystal CVD diamond (SC-CVD) produced at high growth rates has drawn considerable attention (Yan et al., Proc. Nat. Acad. Sci., 2002; Liang et Phys. Lett., 2009). This diamond material can be produced to exhibit a range of optical and mechanical properties, either by optimizing the CVD growth or by post-growth treatment. Specifically, the hardness of the SC-CVD can be significantly enhanced by high-pressure/high-temperature (HPHT) annealing (Yan et al., Phys. Stat. Sol., 2004). This treatment also reduces the measured fracture toughness and provides a means by which to tune the hardness/toughness. Whereas diamond is the hardest material currently known, diamond is also brittle, which limits certain scientific and technological applications. Efforts have been taken to improve the fracture toughness diamond by making diamond/metal composites (Wentorf et al., Science, 1980) and by generating multi-structured diamond material (Anthony et al., Diam. Rel. Mater., 1997).
Diamond has been acknowledged as the hardest material known to man; the intrinsic hardness for natural single crystal diamond is around 100 GPa. As noted above, however, diamond is also known as a brittle material. It has been reported that fracture toughness (K1C) for type Ia diamond is between 7.0 and 8.4 MPa m1/2; for type IIa diamond, K1C is 4.2-5.6 MPa m1/2 (Novikov et al., J. Hard Mater., 1993; Patridge et al., Materials Science and Technology, 1994).
Improvement in growing single crystal CVD diamond (SC-CVD) by MPCVD (Microwave Plasma assisted Chemical Vapor Deposition) process has enabled the fabrication of large size (over 3 ct as commercially available HPHT synthetic Ib diamond), high quality diamonds (Yan et al. Physica. Status. Solidi., 2004; Yan et al., Proceedings of the National Academy of Science, 2002). A gas chemistry including H2/CH4/N2/O2 has been used in the MPCVD process for diamond growth. The (100) growth was significantly enhanced by varying the growth conditions (including substrate temperature, pressure, N2 and O2 flow rate) and the color of the SC-CVD ranges from dark brown, to light brown, to near colorless, to colorless. Ultra high hardness (>150 GPa) and toughness (>30 MPa m1/2) have been reported for such crystals (Yan et al., Physica. Status. Solidi., 2004).
It has also been reported that boron can be preferentially incorporated in the (111) sector in both gem diamonds (Burns et al., J. Cryst. Growth, 1990) and CVD diamond (Miyata et al., J. Mater. Res., 1993). Substitutional boron can expand the diamond lattice by 33.7%, and its solubility in diamond can be as much as 0.9% (Vornov et al. Neorganicheskie Materialy, 1993; Arima et al., J. Crys. Growth, 2007). Boron doped single crystal diamond has been produced by HPHT and CVD processes; however, type IIb diamond with large size (thicker than 2 mm) has not been reported.
U.S. Pat. No. 5,981,057 is directed to a CVD diamond layer containing boron dopant atoms in a concentration of at least 0.05 atomic percent. The diamond layer has an average tensile rupture strength of at least 600 MPa with the nucleation face in tension, and at least 300 MPa with the growth face in tension. Both tensile rupture strengths were measured by a three point bend test on a sample 11 mm in length, 2 mm in width, and with a thickness of 1.4 mm or smaller.
U.S. Pat. No. 7,201,886 is directed to a diamond tool comprising a shaped diamond having at least one layer of single crystal diamond heavily doped to create a visible color. The dopant can be boron.
U.S. Pat. No. 7,160,617 relates to a layer of single crystal boron doped diamond produced by CVD and having a total boron concentration which is uniform.
U.S. Pat. No. 6,858,078 to Hemley et al., which is incorporated herein by reference, is directed to an apparatus and method for diamond production. The disclosed apparatus and method can lead to the production of diamonds that are light brown to colorless.
U.S. patent application Ser. No. 10/889,171, which is incorporated herein by reference, is directed to annealing single-crystal chemical vapor deposition diamonds. Important inventive features include raising the CVD diamond to a set temperature of at least 1500° C. and a pressure of at least 4.0 GPa outside of the diamond stable phase.
U.S. patent application Ser. No. 10/889,170, U.S. Pat. No. 7,115,241, which is herein incorporated by reference, is directed to diamonds with improved hardness. The application discloses a single-crystal diamond with a hardness greater than 120 GPa.
U.S. patent application Ser. No. 10/889,169, now U.S. Pat. No. 7,157,067, which is herein incorporated by reference, is directed to diamonds with improved toughness. The application discloses a single-crystal diamond with a fracture toughness of 11-20 MPam1/2 and a hardness of 50-90 GPa.
U.S. application Ser. No. 11/222,224, which is incorporated by reference, is directed to an annealed single crystal CVD diamond having a high toughness.
The cited references do not relate to single crystal boron-doped CVD diamond that is exceedingly tough. High toughness is a desired quality in single crystal diamond for uses including, but not limited to, micro- and nanomachining and rock drilling. Accordingly, there is an unfulfilled need for single crystal diamond that has a high toughness. Additionally, there is a real need for highly tough single crystal diamond with tunable characteristics, including, but not limited to, color. It is therefore a principal object of this invention to provide such highly tough diamond. Other objects will also be apparent from the detailed description of the invention which follows.